The present invention relates to an automatic transmission, control apparatus and control method for the same, particularly, relates to them preferable for a gear type transmission used in a vehicle.
In recent years, by use of a gear type transmission used for a manual transmission, an automated manual transmission (hereinafter called an “automated MT”) has been developed as a system where operation of a clutch, which is a friction mechanism, and operation of a synchromesh, which is a gear selection mechanism, are automated. In the automated MT, when shifting starts, a clutch for transmitting and cutting off torque of an engine, which is a driving power source, is disengaged, a synchromesh is switched, and then the clutch is engaged again.
Japanese Patent Laid-Open No. 2000-234654 and Japanese Patent Laid-Open No. 2001-295898 discloses a twin clutch type automated MT is known. The twin clutch type automated MT is configured such that two clutches transfer output power (driving torque) from an engine to a transmission alternately. In this twin clutch type automated MT, when shifting starts, one clutch which currently transfers torque before the shifting is gradually disengaged, and the other clutch to be the next gear position is gradually engaged. Then, the driving torque is changed from torque for the gear ratio before the shifting to torque for the gear ratio after the shifting. Therefore, interruption of the driving torque can be avoided, and smooth shifting can be achieved.
In a conventional twin clutch type automated MT, for example, as described in Japanese Patent Laid-Open No. 1998-318361 and Japanese Patent Laid-Open No. 2003-269592, the next gear is predicted to shorten a time for shifting to the next gear position. Then, the transmission input shaft connected to the clutch not used for the current gear change position is selectively connected to a transmission-output shaft by a synchromesh. Accordingly, a predetermined gear position to be predicted next is made standby. This is known as the so-called pre-shift control.
However, in the conventional twin clutch type automated MT, in order to execute the above pre-shift control, the synchromesh for connecting the transmission-input shaft to the transmission-output shaft is frequently used in comparison to the automated MT which is not a twin clutch type. Therefore, deterioration of the synchromesh may be hastened.